Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

The High Albedo of the Hot Jupiter Kepler-7 B

Abstract: Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7 b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44 ± 5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32 ± 0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase light curve with an amplitude of 42 ± 4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. First, we interpret the Kepler-7 b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.

The Bilderberg Model of the Photosphere and Low Chromosphere

Abstract: From 17 through 21 April 1967, an international study week was held in the ‘Bilderberg’ near Arnhem, Netherlands, with the aim of obtaining an internationally acceptable model of the solar photosphere and low chromosphere. It was found that such a model, based on observed intensities and center-to-limb observations of the solar continuous spectrum, could indeed be established. This model, henceforth called the Bilderberg Continuum Atmosphere (BCA), is shown in Table I, which gives the temperature, gas and electron pressures, and other data as functions of the continuous optical depth at 5000 A between τ5000 = 10−7 and 25. The model is characterized by a flat temperature minimum of 4600°K between τ5000 ≈ 10−2 to 10−4. The model is homogeneous, and in hydrostatic equilibrium. A hydrogen-helium ratio of 10 has been assumed.

Planform of mantle convection beneath the Pacific Ocean

Abstract: The correlation between variations of the bathymetry and of the geoid in the Pacific Ocean suggests that both are the surface expression of mantle convection. The planform of the convection which is required to generate the observed anomalies does not consist of rolls but is three dimensional, with rising and sinking jets elongated in the direction of motion of the Pacific plate relative to the frame of reference defined by the hot spots. The spacing between the maxima and minima of the geoid is between 1,500 and 2,000 km and hence favours a model of mantle convection with multiple scales of circulation.

Keck Spectra of Brown Dwarf Candidates and a Precise Determination of the Lithium Depletion Boundary in the α Persei Open Cluster

Abstract: We have identified 27 candidate very low mass members of the relatively young α Persei open cluster from a 6 deg2 CCD imaging survey. Based on their I magnitudes and the nominal age and distance to the cluster, these objects should have masses less than 0.1 ☉ if they are cluster members. We subsequently obtained intermediate-resolution spectra of 17 of these objects using the Keck II telescope and Low-Resolution Imaging Spectrograph (LRIS). We also obtained near-IR photometry for many of the stars. Our primary goal was to determine the location of the "lithium depletion boundary" and, hence, to derive a precise age for the cluster. Most of our program objects have radial velocities consistent with cluster membership, moderately strong Hα emission, and spectral types of M5.5 to M8, as expected from their (R-I)C colors. We detected lithium with equivalent widths greater than or equal to 0.4 A in five of the program objects. We have constructed a color-magnitude diagram for the faint end of the α Persei main sequence, including stars for which high signal-to-noise spectra in the region of the lithium λ6708 absorption line have been obtained. These data allow us to accurately determine the α Persei single-star lithium depletion boundary at M(IC) = 11.47, Mbol = 11.42, (R-I)C0 = 2.12, spectral type M6.0. By reference to theoretical evolutionary models, this converts fairly directly into an age for the α Persei cluster of 90 ± 10 Myr. That age is considerably older than most previously quoted ages for the cluster but consistent with ages estimated from the upper main-sequence turnoff using recent models that include a moderate amount of convective core overshoot. At this age, the two faintest of our spectroscopically confirmed members should be substellar (i.e., brown dwarfs) according to theoretical models.

The host galaxies of gamma-ray bursts. i. interstellar medium properties of ten nearby long-duration gamma-ray burst hosts

Abstract: We present the first observations from a large-scale survey of nearby (z < 1) long-duration gamma-ray burst (LGRB) host galaxies, which consist of eight rest-frame optical spectra obtained at Keck and Magellan. Along with two host galaxy observations from the literature, we use optical emission-line diagnostics to determine metallicities, ionization parameters, young stellar population ages, and star formation rates. We compare the LGRB host environments to a variety of local and intermediate-redshift galaxy populations, as well as the newest grid of stellar population synthesis and photoionization models generated with the Starburst99/Mappings codes. With these comparisons, we investigate whether the GRB host galaxies are consistent with the properties of the general galaxy population, and therefore whether they may be used as reliable tracers of star formation. Despite the limitations inherent in our small sample, we find strong evidence that LGRB host galaxies generally have low-metallicity interstellar medium (ISM) environments out to z ~ 1. The ISM properties of our GRB hosts, including metallicity and ionization parameter, are significantly different from the general galaxy population and host galaxies of nearby broad-lined Type Ic supernovae. However, these properties show better agreement with a sample of nearby metal-poor galaxies.